SOLUTION: Mary and Carol are doing a month project. Carol can do work twice as fast as Mary. If they work together they can finish the project in 4 hours. How long does it take to do the sam

Algebra ->  Rate-of-work-word-problems -> SOLUTION: Mary and Carol are doing a month project. Carol can do work twice as fast as Mary. If they work together they can finish the project in 4 hours. How long does it take to do the sam      Log On


   

Question 885981: Mary and Carol are doing a month project. Carol can do work twice as fast as Mary. If they work together they can finish the project in 4 hours. How long does it take to do the same project?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let Mary's rate of working = +R%5Bm%5D+
in units of ( 1 project ) / ( time to do that project )
Carol's rate = +2R%5Bm%5D+
-----------------------
Add their rates of working to get their rate
working together
+R%5Bm%5D+%2B+2R%5Bm%5D+=+1%2F4+
( the +1%2F4+ is ( 1 project / 4 hrs ) )
-----------------------------------
+3R%5Bm%5D+=+1%2F4+
+R%5Bm%5D+=+1%2F12+
and
+2R%5Bm%5D+=+2%2F12+
+2R%5Bm%5D+=+1%2F6+
-------------------
Mary can do the project in 12 hrs
Carol can do the project in 6 hrs
----------------------------
check:
+1%2F12+%2B+1%2F6+=+1%2F4+
+1%2F12+%2B+2%2F12+=+3%2F12+
+3%2F12+=+3%2F12+
OK